diff --git a/api/tests/Feature/Database/ActivityLogIndexesTest.php b/api/tests/Feature/Database/ActivityLogIndexesTest.php
new file mode 100644
index 00000000..62c9885c
--- /dev/null
+++ b/api/tests/Feature/Database/ActivityLogIndexesTest.php
@@ -0,0 +1,92 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Feature\Database;
+
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Illuminate\Support\Facades\DB;
+use Tests\TestCase;
+
+/**
+ * Regression guard for RFC-WS-7 §3.14 / addendum D-06 composite indexes
+ * on the activity_log table.
+ *
+ * Spatie's activitylog default migration calls nullableMorphs('subject')
+ * and nullableMorphs('causer'), which create composite indexes named
+ * `subject` on (subject_type, subject_id) and `causer` on
+ * (causer_type, causer_id). RFC-WS-7 §3.14 / addendum D-06 require
+ * exactly these indexes for query planner support on activity_log
+ * lookups by morph subject/causer; PR-2 verified they already exist
+ * via information_schema.
+ *
+ * This test fails when:
+ * - A future Spatie major release changes nullableMorphs() semantics.
+ * - A developer rewrites the activity_log migration without keeping
+ *   the morph indexes.
+ * - A new schema-dump regeneration silently drops them.
+ */
+final class ActivityLogIndexesTest extends TestCase
+{
+    use RefreshDatabase;
+
+    public function test_subject_composite_index_exists(): void
+    {
+        $this->assertCompositeIndexExists(
+            table: 'activity_log',
+            columns: ['subject_type', 'subject_id'],
+            description: 'subject composite index (RFC-WS-7 §3.14 / D-06)',
+        );
+    }
+
+    public function test_causer_composite_index_exists(): void
+    {
+        $this->assertCompositeIndexExists(
+            table: 'activity_log',
+            columns: ['causer_type', 'causer_id'],
+            description: 'causer composite index (RFC-WS-7 §3.14 / D-06)',
+        );
+    }
+
+    /**
+     * @param  list<string>  $columns
+     */
+    private function assertCompositeIndexExists(string $table, array $columns, string $description): void
+    {
+        $database = config('database.connections.mysql.database');
+
+        $rows = DB::select(
+            'SELECT INDEX_NAME, COLUMN_NAME, SEQ_IN_INDEX
+             FROM information_schema.STATISTICS
+             WHERE TABLE_SCHEMA = ?
+               AND TABLE_NAME = ?
+             ORDER BY INDEX_NAME, SEQ_IN_INDEX',
+            [$database, $table],
+        );
+
+        $indexColumns = [];
+        foreach ($rows as $row) {
+            $indexColumns[$row->INDEX_NAME][(int) $row->SEQ_IN_INDEX] = $row->COLUMN_NAME;
+        }
+
+        $found = false;
+        foreach ($indexColumns as $sequence) {
+            ksort($sequence);
+            if (array_values($sequence) === $columns) {
+                $found = true;
+                break;
+            }
+        }
+
+        $this->assertTrue(
+            $found,
+            sprintf(
+                'Expected composite index on %s(%s) — %s. Found indexes: %s',
+                $table,
+                implode(', ', $columns),
+                $description,
+                json_encode($indexColumns, JSON_PRETTY_PRINT),
+            ),
+        );
+    }
+}